A critical assessment of the "sterile womb" and "in utero colonization" hypotheses: implications for research on the pioneer infant microbiome.
Level 5 - mechanism / opinion, no new human data
Narrative review and critical methodological assessment (Level 5)
PubMed 28454555 · doi:10.1186/s40168-017-0268-4
What was done
The authors performed a critical narrative review evaluating evidence for the "sterile womb" hypothesis versus the "in utero colonization" hypothesis. They assessed four core domains: anatomical, immunological, and physiological characteristics of the placenta and fetus; molecular methodologies used to examine low-biomass intrauterine samples; neonatal fecal microbiome patterns in the first days of life; and the biological principles underlying the generation of axenic (germ-free) animals.
What was found
The abstract provides no quantitative numbers. The authors found that evidence supporting in utero colonization is weak, driven primarily by molecular assays with inadequate detection limits for low-biomass samples, lack of proper contamination controls, and failure to demonstrate bacterial viability. Additionally, the reliable derivation of axenic mammals via cesarean section supports the sterility of the healthy fetal environment.
Why it matters
This review refutes claims of an in utero microbiome by attributing reported bacterial signals to low-biomass contamination artifacts. It reaffirms the sterile womb paradigm, guiding experimental rigor in neonatal microbiome research and clinical strategies targeting post-birth colonization.
Limits
This is a narrative review without a systematic search methodology, explicit inclusion criteria, or quantitative synthesis. No primary human data, quantitative metrics, or sample sizes are reported in the abstract.
Cited by
- supports Human infants are born sterile and acquire their gut microbiome postnatally from immediate surroundings and parents.